FOXBOROUGH, Mass. -- We didn't learn anything new about Tom Brady in the Patriots' wild 43-40 victory over the Chiefs on Sunday night in Gillette Stadium. Brady is Brady, one of the greatest to ever play the game. It was almost expected he would lead New England to points on each of its four fourth-quarter possessions when the outcome was in doubt, his back-to-back completions of 16 and 19 yards setting up the decisive 28-yard field goal as time expired and giving him the 43rd fourth-quarter/overtime comeback of his 19-year career.

What we didn't know was how Patrick Mahomes, the game's co-headliner, would perform in the face of adversity. To that point, it had been a fairly smooth ride for the 23-year-old wunderkind, who had turned the NFL into his personal playground over the first five weeks of this season. He had rolled over everyone, setting one record after the other and providing enough highlights to fill several "GameDay" shows. But on Sunday night, on a prime-time stage, he threw interceptions in the first and second quarters, trailed 24-9 at the half and was matched against Bill Belichick, the Patriots coach and defensive genius who was 23-0 at home in the regular season against quarterbacks under the age of 25. There were questions about how he would handle the moment.

Then he threw a 67-yard touchdown pass to running back Kareem Hunt on the third play from scrimmage after halftime, capitalizing on a busted coverage. It was the play that sent the snowball down the hill, as Kansas City scored on five of its final six possessions, including a 75-yard strike to Tyreek Hill to tie the score at 40 with 3:03 to play.

Mahomes showed that he's truth in advertising, if not better. He turned early struggles into late-game heroics, matching Brady haymaker for haymaker. As the final seconds ticked off, he stood on the sideline and tugged at the inside of his shoulder pads as Brady moved the Patriots into position for Stephen Gostkowski's winning field goal. The expression on his face hinted at irritation, if not anger. He badly wanted to switch places with his iconic counterpart, saying later: "As a competitor you always want an opportunity."

I learned more about Mahomes in defeat than I did in any of his five victories to open the season, including the first two weeks when he set a league record with 10 touchdown passes. It's easy to succeed when you know the answers to the test beforehand, which almost seemed the case as Mahomes bewildered defenses with his mind, arm talent and ability to throw on the move. But the Patriots confused him early on. Like on his first interception, by linebacker Dont'a Hightower.

"He had come into the line of scrimmage, and I thought he was coming in on a blitz," Mahomes said. "I kind of just lost him. [Tight end Travis Kelce] had beat up his man, so I was trying to get the ball on him as fast as possible to let him go to work with it. [Hightower] had dropped into coverage, and I just didn't see him. He made a great play."

There were other struggles, which made it seem as if it would be one of those nights you chalk up to things not going your way. The Chiefs got inside the New England 25-yard line four times in the first half and came away with only three field goals. The other possession ended with an interception by cornerback Duron Harmon in the end zone.

"Just got a little too greedy," Mahomes said.

At halftime, he was calm and collected. He knew the Chiefs had moved the ball at will, at times, and would get it to start the third quarter. The key would be finishing drives; and, really, what's a 15-point deficit to a team that had scored 30 or more in all but one game?

"When you have the guys that I have on this team, with the weapons that I have, I know that I have to keep slinging it," Mahomes said. "I have to keep putting the ball out there. The offensive line really blocked their tail off and really gave me time to give those guys chances to make plays, and they made plays that whole second half."

After throwing for just 164 yards with no touchdowns and two interceptions in the first half, Mahomes was 9 of 13 for 188 yards and four touchdowns with no INTs in the second half. He was 4 of 5 for 79 yards and two scores in the fourth quarter, when the Chiefs overcame a four-point deficit to lead 33-30 with 8:38 to play, then tied the game on Hill's third scoring reception with just over three minutes to go. If not for the greatness of Brady, Sunday night would have figured prominently in the early lore of Mahomes.

"He is going to be special," Patriots cornerback Jason McCourty said. "We are looking at a rookie (actually a second-year) quarterback who goes out in the first half of the game, throws two picks, and did not blink at all. He came out and played his game and was able to get on the edge a few times and make big plays.

"He was everything we saw on film."

The victory was crucial for the Patriots, who know that the road to another Super Bowl appearance is much easier if it goes through Gillette Stadium. A defeat would have left them three games behind the Chiefs in the loss column and given Kansas City the edge in a tiebreaker should the clubs finish with the same record. But I'm still feeling a bit uneasy if I'm New England, because Mahomes is only going to get better. The mistakes he made in the first half, he likely won't make the next time around. He is known to be a quick study, which partly explains his second-half performance. Also, the Chiefs were without two of their best defensive players in linebacker Justin Houston and safety Eric Berry, who should fill some of the holes that were glaring Sunday night.

Mahomes' presence is why this is the best team coach Andy Reid has had since joining the Chiefs. Their recent history reflects that they start fast and fade in the playoffs, but that's less likely to happen when you have a special young quarterback who, in only his seventh pro start, nearly stared down arguably the greatest quarterback in league history. More impressive: He's wise enough to know he can learn more from a moment like Sunday night than he can in a blowout win.

"You learn a ton," Mahomes said. "First off, you're playing a great opponent in a great atmosphere, and so, just to be able to go against the best, you want to compete against them every single day. We got down, we put ourselves in a huge hole and I'm just proud of my team and how we fought to get back in the game. We had the lead at one point and then we ended up not coming out with the win, but just that fight, it's something you can carry on and to the rest of this season."